Ultrasonic cleaning apparatus

ABSTRACT

An ultrasonic cleaning apparatus which cleans a material at a surface by supplying an ultrasonic wave from an ultrasonic wave application head to a cleaning liquid on the surface, and cleans the surface, wherein the ultrasonic wave application head has an ultrasonic wave transmission member which is provided opposite the surface, and has a curved portion on a first plane placed close to the surface, an ultrasonic transducer which is provided on a second plane placed opposite the first plane of the ultrasonic wave transmission member, and generates and applies an ultrasonic wave to a cleaning liquid on the surface through the ultrasonic wave transmission member, and a preventive portion which is provided in the ultrasonic wave transmission member, and prevents the ultrasonic wave applied to the cleaning liquid and reflected on the surface from entering the ultrasonic transducer through the ultrasonic wave transmission member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 for U.S. Ser. No. 11/159,199, filed Jun. 23, 2005,which is based upon and claims the benefit of priority from priorJapanese Patent Application No. 2004-186500, filed Jun. 24, 2004, theentire contents of each are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ultrasonic cleaning apparatus forcleaning materials such as a semiconductor substrate and glass substrateat a surface by using ultrasonic waves.

2. Description of the Related Art

A process of manufacturing substrates such as semiconductor substrateand glass substrate includes a cleaning step of eliminating particlesadhering to the surface of a substrate. In this cleaning step, anultrasonic cleaning apparatus is used, which eliminates particlesadhering to the surface of the substrate by applying an ultrasonic waveto a cleaning liquid.

Generally, a nozzle type and a slit type are known as an ultrasoniccleaning apparatus. A nozzle type ultrasonic cleaning apparatus cleans amaterial at a surface while rotating the material on a rotary table, andhas a cylindrical cleaning head provided substantially vertical in theupper surface side of the material.

A slit type ultrasonic cleaning apparatus cleans a material at a surfacewhile conveying the material by a conveying unit such as rollers, andhas a bar-shaped cleaning head provided horizontally in the uppersurface side of the material, so as to cross the material conveyingdirection.

These cleaning heads has a liquid chamber inside to store a cleaningliquid, a nozzle or slit on the lower surface to eject the cleaningliquid, and an ultrasonic transducer outside the upper surface to applyan ultrasonic wave to the cleaning liquid in the cleaning chamber.

In the ultrasonic cleaning apparatus configured as above has anultrasonic transducer on the upper surface of the cleaning head, and itis necessary to keep the liquid chamber filled with a cleaning liquid toapply an ultrasonic wave generated by the ultrasonic transducer to thecleaning liquid. Further, it is necessary to keep the liquid chamberfilled with a cleaning liquid to prevent deterioration of the ultrasonictransducer by heat.

However, if the liquid chamber is filled with a cleaning liquid, thecleaning liquid more than the necessary quantity is ejected from thenozzle or slit and much cleaning liquid is wasted.

To solve the above problem, an ultrasonic cleaning apparatus has beendeveloped in recent years, (Jpn. Pat. Appln. KOKAI Publication No.2003-31540).

The ultrasonic cleaning apparatus supplies a cleaning liquid to an uppersurface of a material to be cleaned, and applies an ultrasonic wave tothe cleaning liquid on the upper surface of the material.

The ultrasonic cleaning apparatus has a cylindrical ultrasonic waveapplication head. The ultrasonic wave application head is providedsubstantially vertical to the upper surface of the material, and has anultrasonic lens as a diffusion application means at the lower end, anultrasonic transducer to generate an ultrasonic wave inside, and anozzle to supply a cleaning liquid to the upper surface of a materialoutside.

The ultrasonic lens transmits the ultrasonic wave generated by theultrasonic transducer to the cleaning liquid on the upper surface of thematerial, and has inside a path to flow a cooling liquid to cool theultrasonic transducer. The lower surface of the ultrasonic lens iscurved to swell toward the upper surface of the material to diffuse andapply the ultrasonic wave generated by the ultrasonic transducer to awide area of the cleaning liquid.

According to the ultrasonic cleaning apparatus configured as above,ultrasonic wave is applied directly from the ultrasonic lens to thecleaning liquid supplied to the surface of the material.

Therefore, the material can be cleaned with the least minimum cleaningliquid, and the amount of the cleaning liquid with which the material iscleaned can be decreased. Further, the ultrasonic transducer can becooled by flowing a cooling liquid in the path provided in theultrasonic lens.

As an ultrasonic cleaning apparatus of the type similar to the above,there is a known ultrasonic cleaning apparatus, in which a cylindricalultrasonic lens is provided parallel or substantially parallel to amaterial to be cleaned.

One end of the ultrasonic lens is expanded in the diameter, and theexpanded end face has a block made of material with high thermalconductivity such as copper. A path to flow a cooling liquid is formedinside the block, and an ultrasonic transducer is provided on theoutside surface of the block.

In this ultrasonic cleaning apparatus, an ultrasonic wave generated bythe ultrasonic transducer is transmitted to the ultrasonic lens throughthe block, and vibrates the ultrasonic lens laterally or in thedirection crossing the axial line. This lateral vibration is transmittedto the cleaning liquid between the ultrasonic lens and the material, andused to clean the material at an upper surface.

However, if an ultrasonic wave is applied to a cleaning liquid by usingan ultrasonic lens as described above, an ultrasonic wave generated byan ultrasonic transducer may reflect at an upper surface of a materialto be cleaned and enter an ultrasonic transducer through an ultrasoniclens.

When an ultrasonic wave enters an ultrasonic transducer, the ultrasonictransducer is extremely heated exceeding the cooling effect of a coolingliquid then, the polarization of the ultrasonic transducer may bedeteriorated. In this case, the ultrasonic transducer cannot generate anultrasonic wave with a constant intensity, and decreases the cleaningefficiency.

On the other hand, in the ultrasonic cleaning apparatus in which abar-shaped ultrasonic lens is provided parallel to a material to becleaned and an ultrasonic transducer is provided at one end of the lens,an ultrasonic wave transmission route is not straight, and an ultrasonicwave reflected on the material hardly reaches the ultrasonic transducer.

However, in this ultrasonic cleaning apparatus, the ultrasonic wavegenerated by the ultrasonic transducer is applied to the cleaning liquidafter converting to vibration in the lateral direction of the ultrasoniclens, and the intensity of the ultrasonic wave applied to the cleaningliquid is decreased. Further, since the vibration in the lateraldirection of the ultrasonic lens advances radially around the axial lineof the ultrasonic lens, or toward all directions of the radius of theultrasonic lens, the ultrasonic vibration toward the upper side where nocleaning liquid exists is not effectively used for cleaning thematerial.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided anultrasonic cleaning apparatus comprising an ultrasonic wave applicationhead which cleans a material at a surface by applying an ultrasonic waveto a cleaning liquid supplied to the surface of the material. Theultrasonic wave application head has an ultrasonic wave transmissionmember which is placed opposite to the surface and has a curved portionon a first plane placed close to the surface; an ultrasonic transducerwhich is provided on a second plane opposite to the first plane of theultrasonic transmission member, and generates and applies an ultrasonicwave to a cleaning liquid on the surface through the ultrasonic wavetransmission member; and a preventive portion which is provided in theultrasonic wave transmission member, and prevents the ultrasonic waveapplied to the cleaning liquid and reflected on the surface fromentering the ultrasonic transducer through the ultrasonic wavetransmission member.

According to another aspect of the present invention, there is providedan ultrasonic cleaning apparatus comprising an ultrasonic waveapplication head which cleans a material at a surface by applying anultrasonic wave to a cleaning liquid supplied to the surface of thematerial. The ultrasonic wave application head has an ultrasonic wavetransmission member which is placed opposite to the surface and has acurved portion on a first plane placed close to the surface; anultrasonic transducer which is provided on a second plane opposite tothe first plane of the ultrasonic transmission member, and generates andapplies an ultrasonic wave to the liquid on the surface through thefirst plane of the ultrasonic wave transmission member; and a preventiveportion which is provided in the ultrasonic wave transmission member,and prevents the ultrasonic wave generated by the ultrasonic transducerfrom exiting to the cleaning liquid on the surface at a substantiallyright angle to the surface.

According to another aspect of the present invention, there is providedan ultrasonic cleaning apparatus comprising an ultrasonic waveapplication head which cleans a material at a surface by applying anultrasonic wave to a cleaning liquid supplied to the surface of thematerial. The ultrasonic wave application head has a cylindricalultrasonic wave transmission member with a first plane faced to thesurface, and an ultrasonic transducer which is provided on a secondplane opposite to the first plane of the ultrasonic wave transmissionmember, and applies an ultrasonic wave to the cleaning liquid on thesurface through the ultrasonic wave transmission member,

wherein a portion of the first plane of the ultrasonic wave transmissionmember closest to the surface is circular surrounding the axial line ofthe ultrasonic wave transmission member.

According to another aspect of the present invention, there is providedan ultrasonic cleaning apparatus comprising an ultrasonic waveapplication head which cleans a material at a surface by applying anultrasonic wave to a cleaning liquid supplied to the surface of thematerial. The ultrasonic wave application head has a bar-shapedultrasonic wave transmission member which is placed with an axial lineparallel to the surface and a first plane faced to the surface; and anultrasonic transducer which is provided on a second plane opposite tothe first plane of the ultrasonic transmission member, and generates andapplies an ultrasonic wave to a cleaning liquid on the surface throughthe ultrasonic wave transmission member, wherein a portion of the firstplane of the ultrasonic wave transmission member closest to the surfaceis formed as two linear lines which are located on both sides of a axialline of the ultrasonic wave transmission member respectively.

According to the aspects of the present invention, a high cleaningefficiency can be obtained.

Additional aspects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The aspectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a view showing the configuration of an ultrasonic cleaningapparatus according to a first embodiment of the present invention;

FIG. 2 is a view showing the configuration of an ultrasonic waveapplication head according to the embodiment;

FIG. 3A is a graph showing the intensity distribution of an ultrasonicwave measured under an ultrasonic lens with a notch according to theembodiment;

FIG. 3B is a graph showing the intensity distribution of an ultrasonicwave measured under an ultrasonic lens without a notch according to theembodiment;

FIG. 4A is gradation showing the intensity distribution of an ultrasonicwave measured under an ultrasonic lens with a notch according to theembodiment;

FIG. 4B is gradation showing the intensity distribution of an ultrasonicwave measured under an ultrasonic lens without a notch according to theembodiment;

FIG. 5 is a graph showing the temperatures of an ultrasonic transduceraccording to the embodiment measured by supplying power continuously tothe ultrasonic transducer;

FIG. 6 is a graph showing the temperatures of an ultrasonic transduceraccording to the embodiment measured by supplying power intermittentlyto the ultrasonic transducer;

FIG. 7 is a graph showing the voltage standing wave ratio VSWR whenpower is continuously supplied to the ultrasonic transducer according tothe embodiment;

FIG. 8 is a view showing the configuration of an ultrasonic waveapplication head according to a modification of the embodiment;

FIG. 9 is a perspective view of an ultrasonic cleaning apparatusaccording to a second embodiment of the present invention; and

FIG. 10 is a perspective view of an ultrasonic lens according to amodification of the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Description will be given of the best mode for carrying out the presentinvention.

Embodiment 1

A first embodiment of the present invention will be explained first withreference to FIG. 1-FIG. 8.

[Configuration of Ultrasonic Cleaning Apparatus]

FIG. 1 is a view showing the configuration of an ultrasonic cleaningapparatus according to a first embodiment of the present invention.

As shown in FIG. 1, the ultrasonic cleaning apparatus comprises a spinprocessing unit 10 which holds and rotates a material S such as asemiconductor substrate and glass substrate, and an ultrasonic cleaningunit 20 which supplies a cleaning liquid L to the material S, applies anultrasonic wave to the cleaning liquid L, and cleans the surface of thematerial S.

The spin processing unit 10 has a cylindrical cup body 11 with a bottom.The cup body 11 has an opening 11 a facing upward, and has ejectionports 12 on the bottom 11 b to eject the cleaning liquid L after thecleaning step.

A motor 13 is provided under the cup body 11. A driving shaft 13 a ofthe motor 13 penetrates the bottom wall of the cup body 11, and the midportion of the shaft 13 a is rotatably held by a bearing 14.

A rotary table 15 is provided almost horizontally at the upper end ofthe driving shaft 13 a. Support pins 16 are provided with equalintervals on the upper surface periphery of the rotary table 15. Thesupport pins 16 engage with the periphery of the material S, and supportthe material S substantially horizontally.

The ultrasonic cleaning unit 20 has an ultrasonic wave application head21. The ultrasonic wave application head 21 is placed opposite to thesurface of the material S, and can reciprocate on the surface by drivinga swing arm 22.

[Configuration of Ultrasonic Wave Application Head 21]

FIG. 2 is a view showing the configuration of the ultrasonic waveapplication head 21 according to the embodiment.

As shown in FIG. 2, the ultrasonic wave application head 21 has a headmain body 21 a. The head main body 21 a is formed like a flat plate, andhas an opening 21 b faced to the surface of the material S.

A cylindrical ultrasonic lens 23 (ultrasonic transmission member) isprovided inside the head main body 21 a. The ultrasonic lens 23 is madeof SiO2, for example. The lower end of the ultrasonic lens 23 projectsfrom the opening 21 b of the head main body 21 a to the surface of thematerial S. The lower end face 23 a (first plane) opposite to thesurface of the material S is composed of a curved portion projecting tothe surface as it comes close to the radial center.

The vertical thickness of the ultrasonic lens 23 is set to have thehighest intensity of an ultrasonic wave generated by an ultrasonictransducer 25 (described later) in the ring-like area around an axialline I of the ultrasonic lens 23 when the intensity is measured underthe ultrasonic lens 23.

A notch 24 (preventive portion) is formed at the radial center of thelower end face 23 a of the ultrasonic lens 23. The notch 24 is formed byoblique planes 24 b inclined to the axial line I of the ultrasonic lens23, and formed conical with the diameter becoming small as it goesupward in this embodiment.

As the notch 24 is formed in the ultrasonic lens 23 as described above,the circular area around the axial line I of the lower end face 23 a ofthe ultra-sonic lens 23 becomes closest to the material S.

The ultrasonic transducer 25 is fixed with adhesive to the upper endface 23 c (second surface) of the ultrasonic lens 23. The ultrasonictransducer 25 is made of lead titanate, for example, and generates anultrasonic wave by receiving power from a power supply unit 27. Theultrasonic transducer 25 may also be made of piezoelectric element.

A matching circuit 28 is provided between the power supply unit 27 andultrasonic transducer 25. The matching circuit 28 matches the impedancebetween the power supply unit 27 and ultrasonic transducer 25, and ispreviously adjusted to convert the power from the power supply unit 27most effectively into an ultra-sonic wave in the ultrasonic transducer25.

A nozzle body 26 is provided in the periphery of the head main body 21a. The distal end of the nozzle body 26 is faced to between the lowerend face 23 a of the ultrasonic lens 23 and the surface of the materialS, so that it can supply the cleaning liquid L such as hydrofluoric acidto the surface of the material S.

A cooling tube (not shown) is provided around the ultrasonic lens 23.The cooling tube flows a cooling liquid supplied from a cooling liquidsource (not shown), and can cool the ultrasonic transducer 25 heated bygenerating an ultrasonic wave.

[Effects of Ultrasonic Cleaning Apparatus]

Description will now be given on the effects when the ultrasoniccleaning apparatus configured as described above is used.

When the material S is supported by the support pins 16 on the rotarytable 15, the material S is rotated in the circumferential direction bythe rotary table 15 and the cleaning liquid L is supplied from thenozzle body 26 to the surface of the material S.

When the cleaning liquid L is filled between the ultrasonic lens 23 andthe surface of the material S, the ultrasonic transducer 25 is drivenand an ultra-sonic wave is applied from the ultrasonic lens 23 to thecleaning liquid L on the surface of the material S.

Among the ultrasonic waves applied to the cleaning liquid L, thoseapplied to the cleaning liquid L through the radial center of theultrasonic lens 23 are refracted at the notch 24 formed on the lower endface 23 a of the ultrasonic lens 23.

Thus, the ultrasonic wave is difficult to reach the cleaning liquid Lnear the radial center of the ultrasonic lens 23. As a result, theintensity of the ultrasonic wave applied to the cleaning liquid L isdecreased near the radial center of the ultrasonic lens 23, comparedwith that in the surrounding area.

Among the ultrasonic waves applied to the cleaning liquid L, thoseapplied to the cleaning liquid L not through the radial center of theultrasonic lens 23 are refracted radially around the axial line of theultrasonic lens 23 on the curved surface formed on the lower end face 23a of the ultrasonic lens 23, and applied to a wide area of the cleaningliquid L.

Namely, the ultrasonic wave generated by the ultrasonic transducer 25 isprevented from exiting from the ultrasonic lens 23 substantiallyperpendicular to the surface of the material S, by the notch 24 andcurved surface formed on the lower end face 23 a of the ultrasonic lens23.

FIG. 3A is a graph showing the intensity distribution of the ultrasonicwave measured under the ultrasonic lens 23 with the notch 24 accordingto the embodiment. FIG. 3B is a graph showing the intensity distributionof the ultrasonic wave measured under the ultrasonic lens 23 without thenotch 24 according to the embodiment. In FIG. 3, the solid lineindicates an RMS value, the chain line indicates a peak value, and thedotted line indicates the radial center of the ultrasonic lens 23.

The measuring conditions are as follows.

Generation frequency of ultrasonic wave: 1685[kHz]

Cleaning liquid: Deaerated water

Power supplied to the ultrasonic transducer 25: 15[W]

Output waveform of ultrasonic wave: Continuous wave

According to FIG. 3A and FIG. 3B, it is seen that the intensity of anultrasonic wave is decreased near the radial center of the ultrasoniclens 23 by providing the notch 24 at the radial center on the lower endface 23 a of the ultrasonic lens 23.

FIG. 4A is gradation showing the intensity distribution of theultrasonic wave measured under the ultrasonic lens 23 with the notch 24according to the embodiment. FIG. 4B is gradation showing the intensitydistribution of the ultrasonic wave measured under the ultrasonic lens23 without the notch 24 according to the embodiment.

The measuring conditions are as follows.

Generation frequency of ultrasonic wave: 1685[kHz]

Cleaning liquid: Deaerated water

Power supplied to the ultrasonic transducer 25: 15[W]

Measuring range: Square of 50×50 [mm]

According also to FIG. 4A and FIG. 4B, it is seen that the intensity ofan ultrasonic wave is decreased near the radial center of the ultrasoniclens 23 by providing the notch 24 at the radial center on the lower endface 23 a of the ultrasonic lens 23. It is also seen that the intensityof an ultrasonic wave is increased in the circular area around theradial center of the ultrasonic lens 23 by adjusting the verticalthickness of the ultrasonic lens 23.

The ultrasonic wave applied to the cleaning liquid L is reflected onthat surface of the material S and transmitted to the ultrasonic lens 23(this ultrasonic wave is called a reflected wave hereinafter).

Among the ultrasonic waves reflected on the surface, those transmittedthrough the position out of the radial center of the ultrasonic lens arereflected outside the radial direction of the ultrasonic lens 23 on thecurved surface formed on the lower end face 23 a of the ultrasonic lens23, and most of them do not enter the ultrasonic lens 23.

Among the ultrasonic waves reflected on the surface, those transmittedthrough the radial center of the ultrasonic lens 23 are reflected at thenotch 24 formed on the lower end face 23 a of the ultrasonic lens 23,and most of them do not reach the ultrasonic transducer 25. Even if apart of the reflected wave enters the ultrasonic lens 23, it isrefracted when passing thorough the notch 24 and hardly enter theultrasonic transducer 25 on the ultrasonic lens 23.

Namely, the ultrasonic wave reflected on the surface is prevented fromentering the ultrasonic lens 23 through the ultrasonic lens 23, by thenotch 24 and curved surface formed on the lower end face 23 a of theultrasonic lens 23.

Thus, the ultrasonic transducer 25 is not extremely heated by absorbinga reflected wave, deterioration of polarization is suppressed, andstable cleaning effect can be obtained for a long period of time.

FIG. 5 is a graph showing the temperatures of the ultrasonic transducer25 according to the embodiment measured by supplying power continuouslyto the ultrasonic transducer 25.

In FIG. 5, the solid line indicates the case when the notch 24 is formedin the ultrasonic lens 23, and the chain line indicates the case whenthe notch 24 is not formed. The sign A indicates the case when power of10[W] is supplied to the ultrasonic transducer 25, B indicates the casewhen power of 20[W] is supplied to the ultrasonic transducer 25, and Cindicates the case when power of 30[W] is supplied to the ultrasonictransducer 25, respectively.

The measuring conditions are as follows.

Generation frequency of ultrasonic wave: 1685[kHz]

Cleaning liquid: Deaerated water

Measuring position: Center of the ultrasonic transducer

Sampling: 1[sec]

Comparing the solid line and chain line in FIG. 5, it is seen in anycase of A-C that the temperature of the ultrasonic transducer 25 whenthe notch 24 is formed in the ultrasonic lens 23 is lower than the casewhen the notch 24 is not formed.

FIG. 6 is a graph showing the temperatures of the ultrasonic transducer25 according to the embodiment measured by supplying powerintermittently to the ultrasonic transducer 25. In FIG. 6, the solidline indicates the case when the notch 24 is formed in the ultrasoniclens 23, and the chain line indicates the case when the notch 24 is notformed.

The measuring conditions are as follows.

Generation frequency of ultrasonic wave: 1685[kHz]

Cleaning liquid: Deaerated water

Power supplied to the ultrasonic transducer 25: 20[W]

Measuring position: Center of the ultrasonic transducer 25

Sampling: 1[sec]

Comparing the solid line and chain line in FIG. 6, it is seen that thetemperature of the ultrasonic transducer 25 when the notch 24 is formedon the lower end face 23 a of the ultrasonic lens 23 is about 20% lowerthan the case when the notch 24 is not formed.

According to this experiment, it is seen that even if the ultrasonictransducer 25 is intermittently driven as when actually cleaning thematerial S by using the ultrasonic cleaning apparatus, the temperatureof the ultrasonic transducer 25 is hardly increased when the notch 24 isformed on the lower end face 23 a of the ultrasonic lens 23, comparedwith the case when the notch 24 is not formed.

Besides, if the ultrasonic wave reflected on the surface of the materialS is hardly enter the ultrasonic transducer 25 as in this embodiment,the impedance matching between the ultrasonic transducer 25 and powersupply unit 27 is not disturbed by the reflected wave. Thus, theultrasonic transducer 25 is driven with the matching circuit 28 kept inthe optimum matching state by initial setting, and a desired cleaningeffect can be held.

FIG. 7 is a graph showing the voltage standing wave ratio VSWR whenpower is continuously supplied to the ultrasonic transducer 25 accordingto the embodiment. In FIG. 7, the solid line indicates the case when thenotch 24 is formed in the ultrasonic lens 23, and the chain lineindicates the case when the notch 24 is not formed.

Comparing the solid line and chain line in FIG. 7, it is seen that thevoltage standing wave ratio VSWR when the notch 24 is formed one thelower end face 23 a of the ultrasonic lens 23 is lower than the casewhen the notch 24 is not formed. This indicates that the power suppliedfrom the power supply unit 27 is effectively converted to an ultrasonicwave in the ultrasonic transducer 25.

(Modification of the Embodiment)

FIG. 8 is a view showing the configuration of an ultrasonic waveapplication head 21A according to a modification of the embodiment. Asshown in FIG. 8, a space 24A is taken on the axial line I of theultrasonic lens 23 in this modification, instead of forming the notch 24on the lower end surface 23 a of the ultrasonic lens 23.

Even with this configuration, the ultrasonic wave generated by theultrasonic transducer 25 is prevented from being applied to the cleaningliquid L through the radial center of the ultrasonic lens 23, and theultrasonic wave reflected on the surface is prevented from entering theultrasonic transducer 25 through the ultrasonic lens 23.

It is permitted to bury rubber or similar material on the axial line Iof the ultrasonic lens 23, instead of taking the space 24A. The materialshould not be molten when absorbing an ultrasonic wave.

Embodiment 2

A second embodiment of the present invention will be explained withreference to FIG. 9 and FIG. 10. The same components and effects asthose of the first embodiment will be omitted.

[Configuration of Ultrasonic Cleaning Apparatus]

FIG. 9 is a perspective view of an ultrasonic cleaning apparatusaccording to a second embodiment of the present invention.

As shown in FIG. 9, the ultrasonic cleaning apparatus according to thisembodiment comprises a conveying unit 31 which conveys a material S suchas a semiconductor substrate and glass substrate, and an ultrasonic waveapplication head 32 which supplies a cleaning liquid L to the material Sconveyed by the conveying unit 31, applies an ultrasonic wave to thecleaning liquid L, and cleans the surface of the material S.

[Configuration of Ultrasonic Wave Application Head 32]

The ultrasonic wave application head 32 has a head man body 32 a. Thehead main body 32 a is formed like a long plate, and has an opening 32 bfaced to the surface of the material S.

A bar-shaped ultrasonic lens 33 is provided horizontally inside the headmain body 21 a. The ultrasonic lens 33 is made of SiO2, for example. Thelower end of the ultrasonic lens 33 projects from the opening 32 b ofthe head main body 32 a to the surface of the material S. The lower endface 33 a opposite to the surface of the material S is composed of acurved portion projecting to the surface of the material S as it comesclose to the radial center.

The vertical thickness of the ultrasonic lens 33 is set to have thehighest intensity of an ultrasonic wave generated by an ultrasonictransducer 35 (described later) in the belt-like two areas located onboth sides of the center in the width direction of the ultrasonic lens33 respectively when the intensity is measured under the ultrasonic lens33.

A notch 34 (preventive portion) is formed along the axial line m of theultrasonic lens 33, at the radial center of the lower end face 33 a ofthe ultrasonic lens 33. The notch 34 is formed by two oblique planes 34b inclined to the surface of the material S, and formed like a wedgewith the diameter becoming small as it goes upward in this embodiment.

As the notch 34 is formed in the ultrasonic lens 33 as described above,two linear areas which are located on both sides of the center of thewidth direction of the ultrasonic lens 33 become closest to the materialS.

The ultrasonic transducer 35 is fixed with adhesive to the upper endface 33 b of the ultrasonic lens 33. The ultrasonic transducer 35 ismade of lead titanate, for example, and generates an ultrasonic wave byreceiving power from a power supply unit 37. The ultrasonic transducer35 may also be made of piezoelectric element.

A matching circuit 38 is provided between the power supply unit 37 andultrasonic transducer 35. The matching circuit 38 matches the impedancebetween the power supply unit 37 and ultrasonic transducer 35, and ispreviously adjusted so that the power from the power supply unit 37 ismost effectively converted to an ultrasonic wave in the ultrasonictransducer 35.

A cooling tube (not shown) is provided around the ultrasonic lens 33.The cooling tube is connected to a cooling liquid supply source (notshown), flows a cooling liquid from the cooling liquid source, and coolsthe ultrasonic transducer 35 heated by generating an ultrasonic wave.

The same effects of the first embodiment can be obtained, even if thenotch 34 is formed in the lower end face 33 a of the bar-shapedultrasonic lens 33 as in this embodiment.

(Modification of the Embodiment)

FIG. 10 is a perspective view of an ultrasonic lens according to amodification of the embodiment. As shown in FIG. 10, an elliptical space34A (preventive portion) passing through the center of width directionis taken inside the ultrasonic lens 23 in this modification, instead offorming the notch 34 on the lower end surface 33 a of the ultrasoniclens 33.

Even with this configuration, the ultrasonic wave generated by theultrasonic transducer 35 is prevented from being applied to the cleaningliquid L through the center of width direction of the ultrasonic lens33, and the ultrasonic wave reflected on the surface of the material Sis prevented from entering the ultrasonic transducer 35 through theultrasonic lens 33.

It is permitted to bury rubber or similar material, instead of takingthe space 34A. The material should not be molten when absorbing anultrasonic wave.

The present invention is not limited to the above-mentioned embodiments.The invention may be embodied by modifying the components withoutdeparting from its essential characteristics. The invention may also beembodied in various forms by combining the components disclosed in theabove-mentioned embodiments. For example, some components may be deletedfrom the components used in the above-mentioned embodiments. It is alsopossible to combine the components which are used in differentembodiments.

For example, the ultrasonic transducer 25 may be provided at theposition other than on the upper end face 33 b of the ultrasonic lens23, and the ultrasonic wave generated by the ultrasonic transducer 25may be reflected on the reflection surface provided in the ultrasoniclens 23 and applied to the cleaning liquid L on the surface of thematerial. Even with this configuration, the same effects as theabove-mentioned embodiments can be obtained.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. An ultrasonic cleaning apparatus comprising an ultrasonic waveapplication head which cleans a material at a surface by applying anultrasonic wave to a cleaning liquid supplied to the surface, theultrasonic wave application head comprising: an ultrasonic wavetransmission member which is placed opposite to the surface and has acurved portion on a first plane placed close to the surface; anultrasonic transducer which is provided on a second plane opposite tothe first plane of the ultrasonic transmission member, and generates andapplies an ultrasonic wave to the cleaning liquid on the surface throughthe ultrasonic wave transmission member; and a preventive portion whichis provided in the ultrasonic wave transmission member and prevents theultrasonic wave applied to the cleaning liquid and reflected on thesurface from entering the ultrasonic transducer through the ultrasonicwave transmission member.